According to the scientific poll, 73 percent of self-identified Republicans and 40 percent overall are either don’t believe Obama was born in the U.S. or are not sure.

For both Republicans and Americans overall, belief that Obama is foreign-born was at a high point in September, just 37 days before the Nov. 6 presidential election.

As seen in Table 1 for the full sample and in Table 2 for Republicans only, Berinsky’s conclusions were clear: The percentage of people who think Obama was not born in the United States has held steady throughout the year and perhaps even increased slightly.

“Birtherism is especially pronounced among Republicans,” Berinsky wrote. “Indeed, the level of birtherism among Republicans is the highest it has been this year.”

Table 1: Adam Berinsky birther study: full sample

Table 2: Adam Berinsky birther study: Republicans only

Writing in February, Berinsky noted Obama, since assuming the presidency, had been plagued by rumors that he is not a natural-born citizen and, as a result, is not eligible to serve as president under Article 2, Section 1 of the Constitution.

“These rumors have shown a surprising resilience over the last four years,” Berinsky wrote. “In fact, polls conducted by numerous media organizations repeatedly demonstrated that a significant portion of the American public claimed that Obama was not born in the United States, while many others are not sure if he was.”

Berinsky noted the doubts about where Obama was born have persisted even after the White House released a computer PDF copy of Obama’s long-form birth certificate on April 27, 2011.

“Time and again, the Obama team tried to dispel the “birther” rumor,” he observed.

“During the 2008 presidential contest, Obama released a computer copy of his birth certificate on a campaign website, but it did not quell the controversy. In 2009, Dr. Chiyome Fukino, the director of the Hawaii State Department of Health, verified that Obama was born in Hawaii and is a natural-born citizen. But still the rumors would not die.”